diff -u b/modules/field/FieldInfo.php b/modules/field/FieldInfo.php
--- b/modules/field/FieldInfo.php
+++ b/modules/field/FieldInfo.php
@@ -305,7 +305,7 @@
 
     // Cache miss: collect from the definitions.
 
-    $info = array(
+    $this->bundleInfo[$entity_type][$bundle] = array(
       'instances' => array(),
       'extra_fields' => array(),
     );
@@ -320,7 +320,7 @@
       $field = $fields[$instance['field_name']];
 
       $instance = $this->prepareInstance($instance, $field['type']);
-      $info['instances'][$field['field_name']] = $instance;
+      $this->bundleInfo[$entity_type][$bundle]['instances'][$field['field_name']] = $instance;
 
       // If the field is not in our global "static" list yet, add it.
       if (!isset($this->fieldsById[$field['id']])) {
@@ -338,21 +338,18 @@
     drupal_alter('field_extra_fields', $extra);
     // Merge in saved settings.
     if (isset($extra[$entity_type][$bundle])) {
-      $info['extra_fields'] = $this->prepareExtraFields($extra[$entity_type][$bundle], $entity_type, $bundle);
+      $this->bundleInfo[$entity_type][$bundle]['extra_fields'] = $this->prepareExtraFields($extra[$entity_type][$bundle], $entity_type, $bundle);
     }
 
-    // Save in the "static" cache.
-    $this->bundleInfo[$entity_type][$bundle] = $info;
-
     // The persistent cache additionally contains the definitions of the fields
     // involved in the bundle.
-    $cache = $info + array('fields' => array());
-    foreach ($info['instances'] as $instance) {
+    $cache = $this->bundleInfo[$entity_type][$bundle] + array('fields' => array());
+    foreach ($this->bundleInfo[$entity_type][$bundle]['instances'] as $instance) {
       $cache['fields'][] = $this->fieldsById[$instance['field_id']];
     }
     cache_set("field_info:bundle:$entity_type:$bundle", $cache, 'cache_field');
 
-    return $info;
+    return $this->bundleInfo[$entity_type][$bundle];
   }
 
   /**
diff -u b/modules/field/tests/field.test b/modules/field/tests/field.test
--- b/modules/field/tests/field.test
+++ b/modules/field/tests/field.test
@@ -1274,6 +1274,31 @@
       $this->assertIdentical(field_info_formatter_settings($type), $data['settings'], "field_info_formatter_settings returns {$type}'s formatter settings");
     }
   }
+
+  /**
+   * Tests that the field info cache can be built correctly.
+   */
+  function testFieldInfoCache() {
+    // Create a test field and ensure it's in the array returned by
+    // field_info_fields().
+    $field_name = drupal_strtolower($this->randomName());
+    $field = array(
+      'field_name' => $field_name,
+      'type' => 'test_field',
+    );
+    field_create_field($field);
+    $fields = field_info_fields();
+    $this->assertTrue(isset($fields[$field_name]), 'The test field is initially found in the array returned by field_info_fields().');
+
+    // Now rebuild the field info cache, and set a variable which will cause
+    // the cache to be cleared while it's being rebuilt; see
+    // field_test_entity_info(). Ensure the test field is still in the returned
+    // array.
+    field_info_cache_clear();
+    variable_set('field_test_clear_info_cache_in_hook_entity_info', TRUE);
+    $fields = field_info_fields();
+    $this->assertTrue(isset($fields[$field_name]), 'The test field is found in the array returned by field_info_fields() even if its cache is cleared while being rebuilt.');
+  }
 }
 
 class FieldFormTestCase extends FieldTestCase {
only in patch2:
unchanged:
--- a/modules/field/tests/field_test.entity.inc
+++ b/modules/field/tests/field_test.entity.inc
@@ -9,6 +9,12 @@
  * Implements hook_entity_info().
  */
 function field_test_entity_info() {
+  // If requested, clear the field cache while this hook is being called. See
+  // testFieldInfoCache().
+  if (variable_get('field_test_clear_info_cache_in_hook_entity_info', FALSE)) {
+    field_info_cache_clear();
+  }
+
   $bundles = variable_get('field_test_bundles', array('test_bundle' => array('label' => 'Test Bundle')));
   $test_entity_modes = array(
     'full' => array(